Investment Securities (Summary of Investment Securities with Gross Unrealized Losses) (Details) $ in Thousands	Sep. 30, 2016 USD ($) security	Dec. 31, 2015 USD ($)
Schedule of Investments [Line Items]
Total number of securities, available-for-sale and held-to-maturity | security	2,473
Securities in unrealized loss positions, qualitative disclosure, number of positions | security	598
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 619,427	$ 554,907
Less Than 12 Months, Gross Unrealized Losses	2,872	5,945
12 Months or More, Fair Value	72,966	133,159
12 Months or More, Gross Unrealized Losses	1,014	3,140
Total, Fair Value	692,393	688,066
Total, Gross Unrealized Losses	3,886	9,085
Government sponsored agencies [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	20,532	114,640
Less Than 12 Months, Gross Unrealized Losses	29	292
12 Months or More, Fair Value	17,546	21,681
12 Months or More, Gross Unrealized Losses	385	508
Total, Fair Value	38,078	136,321
Total, Gross Unrealized Losses	414	800
State and political subdivisions [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	391,355	195,285
Less Than 12 Months, Gross Unrealized Losses	2,342	2,891
12 Months or More, Fair Value	29,379	68,361
12 Months or More, Gross Unrealized Losses	188	1,627
Total, Fair Value	420,734	263,646
Total, Gross Unrealized Losses	2,530	4,518
Residential mortgage-backed securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	10,607	169,226
Less Than 12 Months, Gross Unrealized Losses	2	2,146
12 Months or More, Fair Value	8	3,435
12 Months or More, Gross Unrealized Losses	0	76
Total, Fair Value	10,615	172,661
Total, Gross Unrealized Losses	2	2,222
Collateralized mortgage obligations [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	112,890	60,459
Less Than 12 Months, Gross Unrealized Losses	230	408
12 Months or More, Fair Value	20,812	39,382
12 Months or More, Gross Unrealized Losses	162	729
Total, Fair Value	133,702	99,841
Total, Gross Unrealized Losses	392	1,137
Corporate bonds [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	71,912	9,532
Less Than 12 Months, Gross Unrealized Losses	156	200
12 Months or More, Fair Value	4,921	0
12 Months or More, Gross Unrealized Losses	79	0
Total, Fair Value	76,833	9,532
Total, Gross Unrealized Losses	235	200
Preferred stock and trust preferred securities[Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	12,131
Less Than 12 Months, Gross Unrealized Losses	113
12 Months or More, Fair Value	300
12 Months or More, Gross Unrealized Losses	200
Total, Fair Value	12,431
Total, Gross Unrealized Losses	$ 313
US Treasury securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value		5,765
Less Than 12 Months, Gross Unrealized Losses		8
12 Months or More, Fair Value		0
12 Months or More, Gross Unrealized Losses		0
Total, Fair Value		5,765
Total, Gross Unrealized Losses		8
Trust preferred securities [Member]
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value		0
Less Than 12 Months, Gross Unrealized Losses		0
12 Months or More, Fair Value		300
12 Months or More, Gross Unrealized Losses		200
Total, Fair Value		300
Total, Gross Unrealized Losses		$ 200